Method for Producing Group III Nitride Crystal

ABSTRACT

A method for producing a Group III nitride crystal includes the steps of cutting a plurality of Group III nitride crystal substrates  10   p  and  10   q  having a major surface from a Group III nitride bulk crystal  1 , the major surfaces  10   pm  and  10   qm  having a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}, transversely arranging the substrates  10   p  and  10   q  adjacent to each other such that the major surfaces  10   pm  and  10   qm  of the substrates  10   p  and  10   q  are parallel to each other and each [0001] direction of the substrates  10   p  and  10   q  coincides with each other, and growing a Group III nitride crystal  20  on the major surfaces  10   pm  and  10   qm  of the substrates  10   p  and  10   q.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 13/338,263, having a filling date of Dec. 28, 2011. Application Ser. No. 13/338,263 was a continuation of International Application PCT/JP2010/059454, having an international filing date of Jun. 3, 2010. International Application PCT/JP2010/059454 claimed the benefit of priority of Japanese Patent Application No. 2009-154020, filed on Jun. 29, 2009, and the benefit of priority of Japanese Patent Application No. 2009-204979, filed on Sep. 4, 2009. Japanese Patent Application Nos. 2009-154020 and 2009-204979 are each in their entirety hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to methods for producing Group III nitride crystal, and more specifically to methods for producing Group III nitride crystal having a major surface with a plane orientation other than {0001}.

2. Description of the Related Art

Group III nitride crystals suitably used in light emitting devices, electronic devices, and semiconductor sensors are generally produced by crystal growth on a major surface of a sapphire substrate having a (0001) major surface or a GaAs substrate having a (111) A major surface by a vapor-phase growth method, such as a hydride vapor phase epitaxy (HVPE) method or a metalorganic chemical vapor deposition (MOCVD) method, or a liquid-phase growth method, such as a flux method. Thus, Group III nitride crystals generally produced have a major surface with a {0001} plane orientation.

A light emitting device in which a light-emitting layer having a multi-quantum well (MQW) structure is formed on a major surface of a Group III nitride crystal substrate having the major surface with a {0001} plane orientation generates spontaneous polarization in the light-emitting layer because of the polarity of the Group III nitride crystal in a <0001> direction. The spontaneous polarization reduces luminous efficiency. Thus, there is a demand for the production of a Group III nitride crystal having a major surface with a plane orientation other than {0001}.

The following methods have been proposed as a method for producing a Group III nitride crystal having a major surface with a plane orientation other than {0001}. For example, Japanese Unexamined Patent Application Publication No. 2005-162526 (Patent Literature 1) discloses the following method for producing a GaN crystal having a surface with any plane orientation independent of the substrate plane orientation. A plurality of rectangular parallelepiped crystalline masses are cut from a GaN crystal grown by a vapor-phase growth method. After a silicon oxide film is formed on the surface of a sapphire substrate prepared separately, a plurality of depressions reaching the substrate are formed. The plurality of crystalline masses are embedded in the depressions such that the top surfaces of the crystalline masses are unidirectionally oriented. Gallium nitride crystals having a surface with a certain plane orientation are then grown by a vapor-phase growth method using the crystalline masses as seeds.

Japanese Unexamined Patent Application Publication No. 2006-315947 (Patent Literature 2) discloses the following method for producing a nitride semiconductor wafer that can achieve both a low dislocation density and a large area. A primary wafer formed of a hexagonal nitride semiconductor and having two facing main c-planes is prepared. The primary wafer is then cut along an m-plane to produce a plurality of nitride semiconductor bars. The plurality of nitride semiconductor bars are then arranged such that the c-planes of adjacent nitride semiconductor bars face each other and the m-plane of each of the nitride semiconductor bars becomes the top surface. A nitride semiconductor is then regrown on the top surfaces of the arranged nitride semiconductor bars to form a nitride semiconductor layer having a continuous m-plane as the major surface.

Japanese Unexamined Patent Application Publication No. 2008-143772 (Patent Literature 3) discloses the following method for producing a high-crystallinity Group III nitride crystal that has a major surface other than {0001}. A plurality of Group III nitride crystal substrates having a major surface with a certain plane orientation are cut from a Group III nitride bulk crystal. The substrates are then transversely arranged adjacent to each other such that the major surfaces of the substrates are parallel to each other and the substrates have the same [0001] direction. A Group III nitride crystal is then grown on the major surfaces of the substrates.

However, in the method according to Japanese Unexamined Patent Application Publication No. 2005-162526 (Patent Literature 1), in which GaN crystals are grown using crystalline masses of GaN crystals embedded in the sapphire substrate as seeds, a difference in thermal expansion coefficient between sapphire and GaN results in the generation of cracks or strain in the GaN crystals during cooling after crystal growth. Thus, this method could not produce high-crystallinity GaN crystals.

The method according to Japanese Unexamined Patent Application Publication No. 2006-315947 (Patent Literature 2) only produces a nitride semiconductor wafer having an m-plane as a major surface. Furthermore, when a nitride semiconductor layer is grown using the m-plane as a major surface at a high growth rate, polycrystals are deposited on the major surface. It is therefore difficult to produce a thick nitride semiconductor layer having high crystallinity.

In the method according to Japanese Unexamined Patent Application Publication No. 2008-143772 (Patent Literature 3), a Group III nitride crystal is grown on a major surface with a certain plane orientation. Thus, the certain plane orientation includes a plane orientation in which a crystal is stably grown and a plane orientation in which a crystal is unstably grown. In the plane orientation in which a crystal is stably grown, it is difficult to produce a thick Group III nitride crystal because of a low growth rate of the Group III nitride crystal. In the plane orientation in which a crystal is unstably grown, it is difficult to perform stable epitaxial growth of a Group III nitride crystal, and the Group III nitride crystal thus grown tends to have cracks.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to solve the problems described above and provide a method for producing a high-crystallinity Group III nitride crystal having a major surface with a plane orientation other than {0001}, in which the Group III nitride crystal can be grown at a high crystal growth rate.

The present invention provides a method for producing a Group III nitride crystal includes the steps of: cutting a plurality of Group III nitride crystal substrates having a major surface from a Group III nitride bulk crystal, the major surface having a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}; transversely arranging the substrates adjacent to each other such that the major surfaces of the substrates are parallel to each other and the substrates have the same [0001] direction; and growing a Group III nitride crystal on the major surfaces of the substrates.

In a method for producing a Group III nitride crystal according to the present invention, the major surfaces of the substrates may have a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−2−1} and {20−21}. The average roughness Ra of each contact surface of the substrates adjacent to each other may be 50 nm or less. A method for growing the Group III nitride crystal may be a hydride vapor phase epitaxy method.

In the step of growing a Group III nitride crystal of a method for producing a Group III nitride crystal according to the present invention, the crystal growth face of the Group III nitride crystal may be kept flat. In the step of growing a Group III nitride crystal on the major surfaces of the Group III nitride crystal substrates, when the plane orientation of the major surfaces has an off-angle of five degrees or less with respect to {20−21}, the Group III nitride crystal may have a growth rate below 80 μm/h, when the plane orientation of the major surfaces has an off-angle of five degrees or less with respect to {20−2−1}, the Group III nitride crystal may have a growth rate below 90 μm/h, when the plane orientation of the major surfaces has an off-angle of five degrees or less with respect to {22−41}, the Group III nitride crystal may have a growth rate below 60 μm/h, and when the plane orientation of the major surfaces has an off-angle of five degrees or less with respect to {22−4−1}, the Group III nitride crystal may have a growth rate below 80 μm/h.

In the step of growing a Group III nitride crystal of a method for producing a Group III nitride crystal according to the present invention, the Group III nitride crystal may have at least one of the following impurity atom concentrations: an oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and a carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less.

The present invention can provide a method for producing a high-crystallinity Group III nitride crystal having a major surface with a plane orientation other than {0001}, in which the Group III nitride crystal can be grown at a high crystal growth rate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a method for producing a Group III nitride crystal according to an embodiment of the present invention. FIG. 1A illustrates the step of cutting Group III nitride crystal substrates, FIG. 1B illustrates the step of arranging the Group III nitride crystal substrates, FIG. 1C illustrates the step of growing a Group III nitride crystal, and FIG. 1D illustrates the step of growing an additional Group III nitride crystal.

FIG. 2 is a schematic cross-sectional view illustrating a method for producing a Group III nitride crystal according to another embodiment of the present invention. FIG. 2A illustrates the step of cutting Group III nitride crystal substrates, FIG. 2B illustrates the step of arranging the Group III nitride crystal substrates, FIG. 2C illustrates the step of growing a Group III nitride crystal, and FIG. 2D illustrates the step of growing an additional Group III nitride crystal.

FIG. 3 is a schematic cross-sectional view illustrating a method for producing a Group III nitride crystal according to still another embodiment of the present invention. FIG. 3A illustrates the step of cutting Group III nitride crystal substrates, FIG. 3B illustrates the step of arranging the Group III nitride crystal substrates, FIG. 3C illustrates the step of growing a Group III nitride crystal, and FIG. 3D illustrates the step of growing an additional Group III nitride crystal.

FIG. 4 is a schematic cross-sectional view illustrating a method for producing a Group III nitride crystal according to still another embodiment of the present invention. FIG. 4A illustrates the step of cutting Group III nitride crystal substrates, FIG. 4B illustrates the step of arranging the Group III nitride crystal substrates, FIG. 4C illustrates the step of growing a Group III nitride crystal, and FIG. 4D illustrates the step of growing an additional Group III nitride crystal.

FIG. 5 is a schematic view of a base substrate on which a Group III nitride bulk crystal is to be grown. FIG. 5A is a schematic plan view, and FIG. 5B is a schematic cross-sectional view taken along the line VB-VB of FIG. 5A.

DETAILED DESCRIPTION OF THE INVENTION

In crystal geometry, indices (Miller indices), such as (hkl) and (hkil), are used to indicate the plane orientation of a crystal face. The plane orientation of a crystal face of a hexagonal crystal, such as a Group III nitride crystal, is indicated by (hkil), wherein h, k, i, and l are integers called Miller indices and have the relationship of i=−(h+k). A plane with the plane orientation (hkil) is referred to as a (hkil) plane. A direction perpendicular to the (hkil) plane (a direction normal to the (hkil) plane) is referred to as a [hkil] direction. {hkil} denotes a generic plane orientation including (hkil) and plane orientations crystal-geometrically equivalent to (hkil). <hkil> denotes a generic direction including [hkik] and directions crystal-geometrically equivalent to [hkik].

A Group III nitride crystal contains Group III atomic planes and nitrogen atomic planes alternately disposed in the <0001> direction and consequently have polarity in the <0001> direction. In the present application, the crystallographic axis is determined such that the Group III atomic plane is the (0001) plane and the nitrogen atomic plane is the (000−1) plane.

First Embodiment

With reference to FIGS. 1 to 4, a method for producing a Group III nitride crystal according to an embodiment of the present invention includes the following steps: cutting a plurality of Group III nitride crystal substrates 10 p and 10 q having major surfaces 10 pm and 10 qm from a Group III nitride bulk crystal 1, the major surface having a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1} (hereinafter also referred to as a substrate cutting step; see FIGS. 1A to 4A); transversely arranging the Group III nitride crystal substrates 10 p and 10 q adjacent to each other such that the major surfaces 10 pm and 10 qm of the Group III nitride crystal substrates 10 p and 10 q are parallel to each other and each [0001] direction of the Group III nitride crystal substrates 10 p and 10 q is the same (hereinafter also referred to as a substrate arranging step; see FIGS. 1B to 4B); and growing a Group III nitride crystal 20 on the major surfaces 10 pm and 10 qm of the substrates 10 p and 10 q (hereinafter also referred to as a crystal growing step; see FIGS. 1C to 4C).

In accordance with a method for producing a Group III nitride crystal according to the present embodiment, a high-crystallinity Group III nitride crystal having a major surface with a plane orientation other than {0001} can be grown at a high crystal growth rate by growing the Group III nitride crystal on a plurality of Group III nitride crystal substrates 10 p and 10 q having the major surfaces 10 pm and 10 qm with a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}.

A method for producing a Group III nitride crystal according to the present embodiment will be further described in detail below with reference to FIGS. 1 to 4.

With reference to FIGS. 1A to 4A, in the substrate cutting step according to the present embodiment, a plurality of Group III nitride crystal substrates 10 p and 10 q having major surfaces 10 pm and 10 qm are cut from Group III nitride bulk crystal 1. The major surfaces 10 pm and 10 qm have a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}. The term “off-angle,” as used herein, refers to an angle between one plane orientation and the other plane orientation and can be measured by an X-ray diffraction method.

The Group III nitride bulk crystal 1 used in the substrate cutting step is not particularly limited and may be produced by growing a crystal on a major surface of a sapphire substrate having a (0001) major surface or a GaAs substrate having a (111) a-plane as a major surface by a common method, for example, a vapor-phase growth method, such as a HVPE method or a MOCVD method, or a liquid-phase growth method, such as a flux method. Thus, the Group III nitride bulk crystal generally, but not always, has a {0001} major surface. In order to reduce dislocation density and increase crystallinity, the Group III nitride bulk crystal 1 is preferably grown by a facet growth method, as disclosed in Japanese Unexamined Patent Application Publication No. 2001-102307. In the facet growth method, a facet is formed on a plane on which a crystal is to be grown (a crystal growth face) and the crystal is grown without embedding the facet.

A plurality of Group III nitride crystal substrates 10 p and 10 q having the major surfaces 10 pm and 10 qm with a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1} may be cut from the Group III nitride bulk crystal 1 by any method. For example, as illustrated in FIGS. 1A to 4A, the Group III nitride crystal substrates 10 p and 10 q may be cut from the Group III nitride bulk crystal 1 at predetermined intervals along a plurality of planes perpendicular to one of the <20−21> direction, the <20−2−1> direction, the <22−41> direction, and the <22−4−1> direction. (These planes have a plane orientation crystal-geometrically equivalent to one of {20−21}, {20−2−1}, {22−41}, and {22−4−1}. The same applies hereinafter.)

As illustrated in FIGS. 1B to 4B, in the substrate arranging step according to the present embodiment, the plurality of Group III nitride crystal substrates 10 p and 10 q cut out are transversely arranged adjacent to each other such that the major surfaces 10 pm and 10 qm of the substrates 10 p and 10 q are parallel to each other and each [0001] direction of the substrates 10 p and 10 q is the same. In FIGS. 1B to 4B, although reference signs are given to two adjacent Group III nitride crystal substrates 10 p and 10 q of the plurality of Group III nitride crystal substrates, the same applies to other adjacent Group III nitride crystal substrates.

Variations in the angle between the crystallographic axis and the major surfaces of the plurality of Group III nitride crystal substrates 10 p and 10 q within the major surfaces result in a inhomogeneous composition of the Group III nitride crystal grown on the major surfaces of the substrates 10 p and 10 q within planes parallel to the major surfaces of the substrates 10 p and 10 q. The substrates 10 p and 10 q are therefore transversely arranged such that the major surfaces 10 pm and 10 qm of the substrates 10 p and 10 q are parallel to each other. The major surfaces 10 pm and 10 qm of the substrates 10 p and 10 q parallel to each other do not necessarily lie in the same plane. The height difference ΔT (not shown) between the major surfaces 10 pm and 10 qm of the adjacent two Group III nitride crystal substrates 10 p and 10 q is preferably 0.1 mm or less, more preferably 0.01 mm or less.

In order to unidirectionally arrange the crystal orientation of the plurality of Group III nitride crystal substrates 10 p and 10 q to achieve more uniform crystal growth, the substrates 10 p and 10 q are transversely arranged such that each [0001] direction of the substrates 10 p and 10 q is the same. A gap between the plurality of Group III nitride crystal substrates 10 p and 10 q results in low crystallinity of crystals grown on the gap. The Group III nitride crystal substrates 10 p and 10 q are therefore arranged in contact with each other.

With reference to FIGS. 1A to 4A and FIGS. 1B to 4B, the substrate cutting step and the substrate arranging step yield the plurality of Group III nitride crystal substrates 10 p and 10 q from the Group III nitride bulk crystal 1. The Group III nitride crystal substrates 10 p and 10 q are transversely arranged such that the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q are parallel to each other and each [0001] direction of the substrates 10 p and 10 q is the same. The Group III nitride crystal substrates 10 p and 10 q have the major surfaces 10 pm and 10 qm with a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}.

With reference to FIGS. 1C to 4C, in the crystal growing step according to the present embodiment, a Group III nitride crystal 20 is grown on the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q. The Group III nitride crystal 20 is grown by epitaxial growth.

The major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q have a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}. Thus, a major surface 20 m of the Group III nitride crystal 20 epitaxially grown on the major surfaces 10 pm and 10 qm has the same plane orientation as the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q (that is, a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}).

Since the Group III nitride crystal 20 is grown on the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q, and the substrates 10 p and 10 q and the Group III nitride crystal 20 grown have a small difference in thermal expansion coefficient, cracks and strain rarely occur in the Group III nitride crystal 20 during cooling after crystal growth, thus yielding a high-crystallinity Group III nitride crystal.

From the perspective described above, the plurality of Group III nitride crystal substrates 10 p and 10 q and the Group III nitride crystal 20 grown preferably have the same chemical composition. These steps can yield a high-crystallinity Group III nitride crystal 20 having the major surface 20 m with a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}.

In the method for producing a Group III nitride crystal according to the present embodiment, the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q have a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}. Thus, the high-crystallinity Group III nitride crystal 20 having the major surface 20 m with a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1} can be stably grown on the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q at a high crystal growth rate.

The Group III nitride crystal 20 thus formed has a large crystal thickness and consequently a high degree of freedom of cutting direction. Thus, a Group III nitride crystal and a Group III nitride crystal substrate having any plane orientation other than the crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1} can be formed.

When the plane orientation of the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q has an off-angle above five degrees with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}, it is difficult to stably grow a high-crystallinity Group III nitride crystal on the major surfaces 10 pm and 10 qm.

In the method for producing a Group III nitride crystal according to the present embodiment, in order to more stably grow a Group III nitride crystal 20 having higher crystallinity at a higher crystal growth rate, the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q preferably have a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−2−1} and {20−21}.

In the method for producing a Group III nitride crystal according to the present embodiment, each of the contact surfaces (hereinafter referred to as contact surfaces 10 pt and 10 qt) of the plurality of Group III nitride crystal substrates 10 p and 10 q adjacent to each other preferably has an average roughness Ra of 50 nm or less, more preferably 5 nm or less. When each of the contact surfaces 10 pt and 10 qt has an average roughness Ra above 50 nm, a region of the Group III nitride crystal 20 on the neighborhood of the contact surfaces 10 pt and 10 qt (hereinafter referred to as a region-on-substrate-interface 20 t) has low crystallinity.

The region-on-substrate-interface 20 t is disposed on both sides of a vertical plane 20 tc extending upward from one end of the substrate contact surfaces 10 pt and 10 qt. The width ΔW of the region-on-substrate-interface 20 t depends on the average surface roughness Ra of the contact surfaces 10 pt and 10 qt and the growth conditions and crystallinity of the Group III nitride crystal. The width ΔW ranges from approximately 10 to 1000 μm. A region-on-substrate 20 s (A region on the plurality of Group III nitride crystal substrates 10 p and 10 q other than the region-on-substrate-interface. The same applies hereinafter.) And the region-on-substrate-interface 20 t can be differentiated by comparing the full widths at half maximum of X-ray diffraction peaks and/or the threading dislocation densities of the major surfaces in these regions.

The average surface roughness Ra refers to the arithmetical mean roughness Ra defined in JIS B 0601. More specifically, in a portion having a reference length taken from a roughness profile in the direction of an average line, the total of distances between the average line and the roughness profile (absolute deviations) is averaged over the reference length. The average surface roughness Ra can be measured with an atomic force microscope (AFM).

In order for the contact surfaces 10 pt and 10 qt of the plurality of Group III nitride crystal substrates 10 p and 10 q to have an average roughness Ra of 50 nm or less, the method for producing a Group III nitride crystal according to the present embodiment preferably includes the step of grinding and/or polishing side surfaces of the plurality of Group III nitride crystal substrates 10 p and 10 q serving as the contact surfaces 10 pt and 10 qt (hereinafter referred to as a grinding/polishing step) after the substrate cutting step and before the substrate arranging step.

In order to further increase the crystallinity of a Group III nitride crystal to be grown, the method for producing a Group III nitride crystal according to the present embodiment preferably further includes the step of grinding and/or polishing the major surfaces 10 pm and 10 qm, on which a Group III nitride crystal is to be grown, of the plurality of Group III nitride crystal substrates 10 p and 10 q (a grinding/polishing step) after the substrate cutting step and before the substrate arranging step. After the grinding/polishing step, each of the major surfaces 10 pm and 10 qm preferably has a surface roughness of 50 nm or less, more preferably 5 nm or less.

In the method for producing a Group III nitride crystal according to the present embodiment, a method for growing the Group III nitride crystal 20 is not particularly limited and may be a common method, for example, a vapor-phase growth method, such as a HVPE method or a MOCVD method, or a liquid-phase growth method, such as a flux method. Among these production methods, the HVPE method is preferred because of a high crystal growth rate.

With reference to FIGS. 1C to 4C, the left side of a central wavy line indicates the case where the Group III nitride crystal 20 grows and forms a flat major surface 20 m while a crystal growth face 20 g is kept flat, and the right side of the central wavy line indicates the case where the Group III nitride crystal 20 grows while forming a plurality of facets 20 gf on the crystal growth face 20 g and forms a major surface 20 m having a plurality of facets 20 mf.

With reference to the left side of the central wavy line in FIGS. 1C to 4C, in the step of growing a Group III nitride crystal in the method for producing a Group III nitride crystal according to the present embodiment, the Group III nitride crystal 20 is preferably grown while the crystal growth face 20 g is kept flat. The clause “the crystal growth face 20 g is kept flat,” as used herein, means that the crystal growth face 20 g is substantially flat and forms no facet 20 gf.

In the step of growing a Group III nitride crystal according to the present embodiment, the Group III nitride crystal 20 is grown on the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q. The major surfaces 10 pm and 10 qm have a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}. The Group III nitride crystal grows in one of the <20−21> direction, the <20−2−1> direction, the <22−41> direction, and the <22−4−1> direction. The Group III nitride crystal 20 grown in that direction tends to have a planar defect in the {0001} plane (since the (0001) in-plane and the (000−1) in-plane are the same in-plane, they are hereinafter collectively referred to as the {0001} in-plane) and low crystallinity.

With reference to the right side of the central wavy line in FIGS. 1C to 4C, a particular increase in the growth rate of the Group III nitride crystal 20 results in the formation of a plurality of facets 20 gf on the crystal growth face 20 g, which is accompanied by an increase in the density of planar defects in the {0001} plane, resulting in low crystallinity.

Thus, in the growth of the Group III nitride crystal 20, keeping the crystal growth face 20 g flat without forming a plurality of facets 20 gf on the crystal growth face 20 g can reduce the density of planar defects in the {0001} plane of the Group III nitride crystal 20 grown, thereby yielding a high-crystallinity Group III nitride crystal. The density of planar defects in the {0001} plane of the Group III nitride crystal may be determined by cathodoluminescence (CL) of a cross section perpendicular to the direction of the major surface of the Group III nitride crystal tilting from the (0001) plane or the (000−1) plane.

In the growth of the Group III nitride crystal 20, the crystal growth face 20 g can be kept flat at a growth rate of the Group III nitride crystal 20 below a predetermined rate. The growth rate at which the crystal growth face 20 g can be kept flat depends on the plane orientation of the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q as described below. When the plane orientation of the major surfaces of the Group III nitride crystal substrates has an off-angle of five degrees or less with respect to {20−21}, the growth rate of the Group III nitride crystal is below 80 μm/h. When the plane orientation of the major surfaces of the Group III nitride crystal substrates has an off-angle of five degrees or less with respect to {20−2−1}, the growth rate of the Group III nitride crystal is below 90 μm/h. When the plane orientation of the major surfaces of the Group III nitride crystal substrates has an off-angle of five degrees or less with respect to {22−41}, the growth rate of the Group III nitride crystal is below 60 μm/h. When the plane orientation of the major surfaces of the Group III nitride crystal substrates has an off-angle of five degrees or less with respect to {22−4−1}, the growth rate of the Group III nitride crystal is below 80 μm/h.

In the growth of a Group III nitride crystal, when the growth rate of the Group III nitride crystal 20 is equal to or more than the predetermined rate, a plurality of facets 20 gf are formed on the crystal growth face 20 g of the Group III nitride crystal 20. The plurality of facets 20 gf have the shape of a plurality of stripes. Each of the stripe-shaped facets 20 gf extends in a direction perpendicular to the direction of the crystal growth face 20 g tilting from the (0001) plane or the (000−1) plane. Each stripe of the facets 20 gf has a width and a depth in the range of approximately 2 to 300 μm. The formation of the facets 20 gf on the crystal growth face 20 g during the growth of the Group III nitride crystal 20 causes planar defects in the {0001} plane of the Group III nitride crystal 20, thus decreasing crystallinity. A plurality of facets 20 mf formed on the major surface 20 m of the Group III nitride crystal 20 during such growth have a shape, a direction, a width, and a depth similar to those of the plurality of facets 20 gf formed on the crystal growth face 20 g. The Group III nitride crystal 20 has depressions 20 v formed of the plurality of facets 20 mf in the major surface 20 m.

In the step of growing a Group III nitride crystal, a Group III nitride crystal 20 having at least one of the following impurity atom concentrations is preferably grown: an oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and a carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. The concentrations of the impurity atoms of a Group III nitride crystal, such as an oxygen atom, a silicon atom, a hydrogen atom, and a carbon atom can be measured by secondary ion mass spectrometry (hereinafter also referred to as SIMS).

Setting at least one impurity concentration of the oxygen atom concentration, the silicon atom concentration, the hydrogen atom concentration, and the carbon atom concentration of a Group III nitride crystal to the predetermined concentration described above can reduce the density of planar defects in the {0001} plane, yielding a high-crystallinity Group III nitride crystal. Coalescence of dislocations in the growth of a Group III nitride crystal reduces the number of dislocations and the volume of the crystal, thereby warping the crystal and increasing planar defects. Setting the impurity atom concentration to the predetermined concentration described above probably reduces the decrease in crystal volume, reducing the density of planar defects. At an impurity atom concentration below the predetermined concentration, the decrease in crystal volume cannot probably be reduced, which makes it difficult to reduce the formation of planar defects in the {0001} plane. On the other hand, at an impurity atom concentration above the predetermined concentration, impurity atoms are probably condensed in the (0001) plane, making it difficult to reduce the formation of planar defects in the {0001} plane.

From the perspective described above, the oxygen atom concentration is more preferably 5×10¹⁶ cm⁻³ or more and 1×10¹⁹ cm⁻³ or less, still more preferably 1×10¹⁷ cm⁻³ or more and 8×10¹⁸ cm⁻³ or less. The silicon atom concentration is more preferably 1×10¹⁵ cm⁻³ or more and 3×10¹⁸ cm⁻³ or less, still more preferably 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. The hydrogen atom concentration is more preferably 1×10¹⁷ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less, still more preferably 2×10¹⁷ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less. The carbon atom concentration is more preferably 5×10¹⁶ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less, still more preferably 9×10¹⁶ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less.

In order to further reduce the formation of planar defects in the {0001} plane during the growth of a Group III nitride crystal, more preferably two, still more preferably three, most preferably four, of the impurity atom concentrations described above (the oxygen atom concentration, the silicon atom concentration, the hydrogen atom concentration, and the carbon atom concentration) satisfy the predetermined concentrations.

In a method for growing a Group III nitride crystal, an impurity atom may be added to a Group III nitride crystal by any method, including the following methods. Oxygen atoms may be added using O₂ gas (oxygen gas), O₂ gas diluted with an inert gas, such as N₂ gas, Ar gas, or He gas, a carrier gas (such as H₂ gas or N₂ gas) containing H₂O, or a raw material gas (such as HCl gas or NH₃ gas) containing H₂O. A quartz container may be used as a crystal growth container to allow quartz of the reaction vessel to react with a raw material NH₃ gas, producing H₂O gas to be used. Silicon atoms may be added using a silicon compound gas, such as SiH₄ gas, SiH₃Cl gas, SiH₂Cl₂ gas, SiHCl₃ gas, SiCl₄ gas, or SiF₄. A quartz container may be used as a crystal growth container to allow quartz of the reaction vessel to react with a raw material NH₃ gas, producing a silicon-containing gas to be used. Hydrogen atoms may be added using a gas mixture of a carrier gas, such as H₂ gas, and an inert gas, such as N₂ gas, Ar gas, or He gas. Carbon atoms may be added using a carbon compound gas, such as CH₄ gas. A carbon material (for example, a carbon plate) may be placed in a crystal growth container to allow carbon of the carbon material to react with hydrogen gas serving as a carrier gas or HN₃ gas serving as a raw material gas, producing a carbon-containing gas to be used.

A method for preventing the contamination of a Group III nitride crystal with an impurity atom may be the following method. The contamination with oxygen atoms and silicon atoms may be prevented by not using a gas containing oxygen atoms and silicon atoms and covering the inner wall of a crystal growth container containing oxygen atoms and/or silicon atoms with a material containing neither oxygen atoms nor silicon atoms, such as BN. The contamination with hydrogen atoms may be prevented by not using a carrier gas containing hydrogen gas. The contamination with carbon atoms may be prevented by using neither a carbon material nor a gas containing carbon atoms.

With reference to FIGS. 1C to 4C and FIGS. 1D to 4D, a method for producing a Group III nitride crystal according to the present embodiment may include the steps of preparing an additional Group III nitride crystal substrate 20 p having a major surface 20 pm from the Group III nitride crystal 20 grown as described above, the major surface 20 pm having a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}, and growing an additional Group III nitride crystal 30 on the major surface 20 pm of the additional Group III nitride crystal substrate 20 p. These steps can yield an additional high-crystallinity Group III nitride crystal 30 having the major surface 30 m with a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}.

The step for preparing an additional Group III nitride crystal substrate 20 p is not particularly limited and may be performed by cutting a plane parallel to the major surfaces 10 pm and 10 qm of the plurality of Group III nitride crystal substrates 10 p and 10 q from the Group III nitride crystal 20 grown. In order to grow an additional Group III nitride crystal 30 having high crystallinity on the major surface 20 pm, the major surface 20 pm of the additional Group III nitride crystal substrate 20 p thus cut out preferably has an average roughness Ra of 50 nm or less, more preferably 5 nm or less. In order for the major surface 20 pm of the Group III nitride crystal substrate 20 p to have an average roughness Ra of 50 nm or less, after the Group III nitride crystal substrate 20 p is cut out and before the additional Group III nitride crystal 30 is grown, the major surface 20 pm of the Group III nitride crystal substrate 20 p is preferably ground and/or polished.

In the method for producing a Group III nitride crystal according to the present embodiment, a method for growing the additional Group III nitride crystal 30 is not particularly limited and may be a common method, for example, a vapor-phase growth method, such as a HVPE method or a MOCVD method, or a liquid-phase growth method, such as a flux method. Among these production methods, the HVPE method is preferred because of a high crystal growth rate.

With reference to FIGS. 1D to 4D, the left side of a central wavy line indicates the case where the Group III nitride crystal 30 grows and forms a flat major surface 30 m while a crystal growth face 30 g is kept flat, and the right side of the central wavy line indicates the case where the Group III nitride crystal 30 grows while forming a plurality of facets 30 gf on the crystal growth face 30 g and forms a major surface 30 m having a plurality of facets 30 mf.

With reference to the left side of the central wavy line in FIGS. 1D to 4D, in the step of growing an additional Group III nitride crystal in the method for producing a Group III nitride crystal according to the present embodiment, the additional Group III nitride crystal 30 is preferably grown while the crystal growth face 30 g is kept flat. The clause “the crystal growth face 30 g is kept flat,” as used herein, means that the crystal growth face 30 g is substantially flat and forms no facet 30 gf.

Also in the growth of the additional Group III nitride crystal 30 according to the present embodiment, the additional Group III nitride crystal 30 grown in one of the <20−21> direction, the <20−2−1> direction, the <22−41> direction, and the <22−4−1> direction tends to have a planar defect in the {0001} plane and low crystallinity.

With reference to the right side of the central wavy line in FIGS. 1D to 4D, a particular increase in the growth rate of the additional Group III nitride crystal 30 results in the formation of a plurality of facets 30 gf on the crystal growth face 30 g, which is accompanied by an increase in the density of planar defects in the {0001} plane, resulting in low crystallinity.

Thus, in the growth of the additional Group III nitride crystal 30, keeping the crystal growth face 30 g flat without forming a plurality of facets 30 gf on the crystal growth face 30 g can reduce the density of planar defects in the {0001} plane of the additional Group III nitride crystal 30 grown, thereby yielding a high-crystallinity Group III nitride crystal.

In the growth of the additional Group III nitride crystal 30, the crystal growth face 30 g can be kept flat at a growth rate of the additional Group III nitride crystal 30 below a predetermined rate. The growth rate at which the crystal growth face 30 g can be kept flat depends on the plane orientation of the major surface 20 pm of the additional Group III nitride crystal substrate 20 p as described below. When the plane orientation of the major surface of the additional Group III nitride crystal substrate has an off-angle of five degrees or less with respect to {20−21}, the growth rate of the additional Group III nitride crystal is below 140 μm/h. When the plane orientation of the major surface of the additional Group III nitride crystal substrate has an off-angle of five degrees or less with respect to {20−2−1}, the growth rate of the additional Group III nitride crystal is below 150 μm/h. When the plane orientation of the major surface of the additional Group III nitride crystal substrate has an off-angle of five degrees or less with respect to {22−41}, the growth rate of the additional Group III nitride crystal is below 120 μm/h. When the plane orientation of the major surface of the additional Group III nitride crystal substrate has an off-angle of five degrees or less with respect to {22−4−1}, the growth rate of the additional Group III nitride crystal is below 140 μm/h.

Thus, even at a high crystal growth rate, the crystal growth face is more easily kept flat in the growth of the additional Group III nitride crystal 30 than in the growth of the Group III nitride crystal 20. This is probably because the Group III nitride crystal 20 is grown on the major surfaces 10 pm and 10 qm of the adjacent Group III nitride crystal substrates 10 p and 10 q whereas the additional Group III nitride crystal 30 is grown on the major surface 20 pm of the additional Group III nitride crystal substrate 20 p and can consequently be grown more uniformly over the entire surface of the substrate.

In the growth of the additional Group III nitride crystal, when the growth rate of the additional Group III nitride crystal 30 is equal to or more than the predetermined rate, a plurality of facets 30 gf are formed on the crystal growth face 30 g of the additional Group III nitride crystal 30. The plurality of facets 30 gf have the shape of a plurality of stripes. Each of the stripe-shaped facets 30 gf extends in a direction perpendicular to the direction of the crystal growth face 30 g tilting from the (0001) plane or the (000−1) plane. Each stripe of the facets 30 gf has a width and a depth in the range of approximately 2 to 300 μm. The formation of the facets 20 gf on the crystal growth face 20 g during the growth of the Group III nitride crystal 20 causes planar defects in the {0001} plane of the Group III nitride crystal 20, thus decreasing crystallinity. A plurality of facets 30 mf formed on the major surface 30 m of the Group III nitride crystal 30 during growth have a shape, a direction, a width, and a depth similar to those of the plurality of facets 30 gf formed on the crystal growth face 30 g. The Group III nitride crystal 30 has depressions 30 v formed of the plurality of facets 30 mf in the major surface 30 m.

In the step of growing the additional Group III nitride crystal 30, as in the growth of the Group III nitride crystal 20, the Group III nitride crystal 30 having at least one of the following impurity atom concentrations is preferably grown: an oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and a carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less.

From the perspective described above, with respect to the impurity atom concentration of the Group III nitride crystal 30, the oxygen atom concentration is more preferably 5×10¹⁶ cm⁻³ or more and 1×10¹⁹ cm⁻³ or less, still more preferably 1×10¹⁷ cm⁻³ or more and 8×10¹⁸ cm⁻³ or less. The silicon atom concentration is more preferably 1×10¹⁵ cm⁻³ or more and 3×10¹⁸ cm⁻³ or less, still more preferably 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. The hydrogen atom concentration is more preferably 1×10¹⁷ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less, still more preferably 2×10¹⁷ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less. The carbon atom concentration is more preferably 5×10¹⁶ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less, still more preferably 9×10¹⁶ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less. More preferably two, still more preferably three, most preferably four, of the impurity atom concentrations described above (the oxygen atom concentration, the silicon atom concentration, the hydrogen atom concentration, and the carbon atom concentration) satisfy the predetermined concentrations.

In a method for growing an additional Group III nitride crystal, a method for adding an impurity atom to the additional Group III nitride crystal 30 and a method for preventing the contamination of the additional Group III nitride crystal 30 with an impurity atom are not particularly limited. The methods described for the growth of the Group III nitride crystal 20 can be used.

In the growth of an additional Group III nitride crystal, a region-on-substrate 30 s of the additional Group III nitride crystal 30 can be formed on the region-on-substrate 20 s of the additional Group III nitride crystal substrate 20 p, and a region-on-substrate-interface 30 t of the additional Group III nitride crystal 30 can be formed on the region-on-substrate-interface 20 t of the additional Group III nitride crystal substrate 20 p.

Second Embodiment

With reference to FIGS. 1 to 4, a Group III nitride crystal according to another embodiment of the present invention is Group III nitride crystals 20 and 30 having a major surface with a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}. The Group III nitride crystals 20 and 30 have at least one of the following impurity atom concentrations: an oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and a carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less.

The Group III nitride crystals 20 and 30 according to the present embodiment have major surfaces 20 m and 30 m with a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}. In a light emitting device in which a light-emitting layer having a multi-quantum well (MQW) structure is formed on the major surfaces 20 m and 30 m of the Group III nitride crystals 20 and 30 serving as a substrate, therefore, spontaneous polarization in the light-emitting layer is prevented. This reduces a decrease in luminous efficiency. The Group III nitride crystals according to the present embodiment have at least one of the following impurity concentrations: an oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and a carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. Thus, the Group III nitride crystals according to the present embodiment have high crystallinity due to a reduced formation of planar defects in the {0001} plane.

The Group III nitride crystals 20 and 30 according to the present embodiment have the major surfaces 20 m and 30 m preferably having an area of 10 cm² or more, more preferably 18 cm² or more, still more preferably 40 cm² or more. The Group III nitride crystals thus obtained have a large size and high crystallinity.

EXAMPLES Preparation of Group III Nitride Bulk Crystal

A GaN bulk crystal, which is a Group III nitride bulk crystal for use in a method for producing a Group III nitride crystal according to the present invention, was produced by the following method, with reference to FIG. 5.

First, a SiO₂ layer having a thickness of 100 nm was formed as a mask layer 91 on a base substrate 90 by sputtering. The base substrate 90 was a GaAs substrate having a (111) a-plane as a major surface and had a diameter of 50 mm and a thickness of 0.8 mm. As illustrated in FIGS. 5A and B, a pattern was then formed by a photolithography method and etching. In the pattern, windows 91 w having a diameter D of 2 μm were hexagonally close-packed at intervals P of 4 μm. The GaAs substrate (the base substrate 90) was exposed from the windows 91 w.

A GaN bulk crystal, which is a Group III nitride bulk crystal, was grown on the GaAs substrate (the base substrate 90), on which the mask layer 91 having a plurality of windows 91 w was formed, by a HVPE method. More specifically, a GaN low-temperature layer having a thickness of 80 nm was grown at 500° C. on the GaAs substrate by the HVPE method. A GaN intermediate layer having a thickness of 60 μm was then grown at 950° C. A GaN bulk crystal having a thickness of 5 mm was then grown at 1050° C.

The GaAs substrate was then removed from the GaN bulk crystal by etching using aqua regia to form a GaN bulk crystal having a diameter of 50 mm and a thickness of 3 mm, which is a Group III nitride bulk crystal.

Example 1

First, with reference to FIG. 1A, both major surfaces, a (0001) plane and a (000−1) plane, of a GaN bulk crystal (a Group III nitride bulk crystal 1) were ground and polished to an average roughness Ra of 5 nm. The average surface roughness Ra was determined with AFM.

With reference to FIG. 1A, the GaN bulk crystal (the Group III nitride bulk crystal 1) in which the average roughness Ra of each of the major surfaces was 5 nm was cut perpendicularly to the <20−21> direction into a plurality of GaN crystal substrates (Group III nitride crystal substrates 10 p and 10 q). The GaN crystal substrates had a width S of 3.1 mm, a length L in the range of 20 to 50 mm, and a thickness T of 1 mm and had a {20−21} major surface. The four planes of each of the GaN crystal substrates not yet subjected to grinding and polishing were ground and polished to an average roughness Ra of 5 nm. Thus, a plurality of GaN crystal substrates were prepared in which the average roughness Ra of the {20−21} major surface was 5 nm. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {20−21}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {20−21}. The off-angle was determined by an X-ray diffraction method.

With reference to FIG. 1B, the plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (20−21) major surfaces 10 pm and 10 qm of the GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) were parallel to each other and each [0001] direction of the GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) coincided with each other. Also with reference to FIG. 1C, each of contact surfaces 10 pt and 10 qt of the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

With reference to FIG. 1C, the (20−21) major surfaces 10 pm and 10 qm of the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) arranged in the quartz crystal growth container were treated at 800° C. for two hours in a mixed gas atmosphere of 10% by volume hydrogen chloride gas and 90% by volume nitrogen gas. A GaN crystal (a Group III nitride crystal 20) was then grown on the major surfaces 10 pm and 10 qm by a HVPE method at a crystal growth temperature of 1020° C. for 40 hours.

The GaN crystal (the Group III nitride crystal 20) had a thickness of 2.4 mm, as determined by a contact thickness gauge (Digimatic Indicator manufactured by Mitutoyo Co.). Thus, the crystal growth rate was 60 μm/h. With reference to the left side of the central portion in FIG. 1C, the GaN crystal (the Group III nitride crystal 20) had no abnormal crystal growth in a region-on-substrate-interface 20 t and a region-on-substrate 20 s and had a flat (20−21) major surface 20 m. The crystallinity of the GaN crystal (the Group III nitride crystal 20) was determined by the X-ray rocking curve measurement of the (20−21) plane. In the region-on-substrate 20 s of the GaN crystal, an unsplit diffraction peak having a full width at half maximum of 100 arcsec was observed. In the region-on-substrate-interface 20 t having a width ΔW of 300 μm, a split diffraction peak having a full width at half maximum of 300 arcsec was observed.

The (20−21) major surface 20 m of the GaN crystal had a threading dislocation density of 1×10⁷ cm⁻² in the region-on-substrate 20 s and 3×10⁷ cm⁻² in the region-on-substrate-interface 20 t, as determined by cathodoluminescence (hereinafter referred to as CL). The planar defect density in the {0001} plane of the GaN crystal was determined to be 8.3 cm⁻¹ by cathodoluminescence (CL) of a cross section of the GaN crystal perpendicular to the <1−210> direction. The GaN crystal had a carrier concentration of 5×10¹⁸ cm⁻³ as calculated from the Hall measurement. The concentrations of the main impurity atoms of the GaN crystal were measured by secondary ion mass spectrometry (SIMS)) as follows: the oxygen atom concentration [O] was 5×10¹⁸ cm⁻³, the silicon atom concentration [Si] was 1×10¹⁸ cm⁻³, the hydrogen atom concentration [H] was 4×10¹⁶ cm⁻³, and the carbon atom concentration [C] was 5×10¹⁵ cm⁻³. Table I summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (20−21) in Example 1, substantially the same results were obtained even in the case that at least part of the plane orientations were (−2201) (which is crystal-geometrically equivalent with (20−21)).

Example 2

First, with reference to FIG. 2A, both major surfaces, a (0001) plane and a (000−1) plane, of a GaN bulk crystal (a Group III nitride bulk crystal 1) were ground and polished to an average roughness Ra of 5 nm.

With reference to FIG. 2A, the GaN bulk crystal (the Group III nitride bulk crystal 1) in which the average roughness Ra of each of the major surfaces was 5 nm was cut perpendicularly to the <20−2−1> direction into a plurality of GaN crystal substrates (Group III nitride crystal substrates 10 p and 10 q). The GaN crystal substrates had a width S of 3.1 mm, a length L in the range of 20 to 50 mm, and a thickness T of 1 mm and had a {20−2−1} major surface. Four planes of each of the GaN crystal substrates not subjected to grinding and polishing were ground and polished to an average roughness Ra of 5 nm. Thus, a plurality of GaN crystal substrates were prepared in which the average roughness Ra of the {20−2−1} major surface was 5 nm. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {20−2−1}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {20−2−1}.

With reference to FIG. 2B, the plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (20−2−1) major surfaces 10 pm and 10 qm of the GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) were parallel to each other and each [0001] direction of the GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) coincided with each other. Also with reference to FIG. 2C, each of contact surfaces 10 pt and 10 qt of the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

With reference to FIG. 2C, the (20−2−1) major surfaces 10 pm and 10 qm of the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) arranged in the quartz crystal growth container were treated in the same way as in Example 1. A GaN crystal (a Group III nitride crystal 20) was then grown on the major surfaces 10 pm and 10 qm by the same growth method at the same growth temperature for the same growth time as in Example 1.

The GaN crystal (the Group III nitride crystal 20) had a thickness of 3.2 mm, and the crystal growth rate was 80 μm/h. With reference to the left side of the central portion in FIG. 2C, the GaN crystal (the Group III nitride crystal 20) had no abnormal crystal growth in a region-on-substrate-interface 20 t and a region-on-substrate 20 s and had a flat (20−2−1) major surface 20 m. The crystallinity of the GaN crystal (the Group III nitride crystal 20) was determined by the X-ray rocking curve measurement of the (20−2−1) plane. In the region-on-substrate 20 s, an unsplit diffraction peak having a full width at half maximum of 90 arcsec was observed. Thus, this GaN crystal had better crystallinity than the GaN crystal having the (20−21) plane as the major surface. In the region-on-substrate-interface 20 t having a width ΔW of 100 μm, a split diffraction peak having a full width at half maximum of 360 arcsec was observed.

The (20−2−1) major surface 20 m of the GaN crystal had a threading dislocation density of 1×10⁷ cm⁻² in the region-on-substrate 20 s and 4×10⁷ cm⁻² in the region-on-substrate-interface 20 t. The planar defect density in the {0001} plane of the GaN crystal was determined to be 6.1 cm⁻¹ by cathodoluminescence (CL) of a cross section of the GaN crystal perpendicular to the <1−210> direction. The GaN crystal had a carrier concentration of 1×10¹⁸ cm⁻³ as calculated from the Hall measurement. The concentrations of the main impurity atoms of the GaN crystal were measured by secondary ion mass spectrometry (SIMS)) as follows: the oxygen atom concentration [O] was 9×10¹⁷ cm⁻³, the silicon atom concentration [Si] was 1×10¹⁸ cm⁻³, the hydrogen atom concentration [H] was 4×10¹⁶ cm⁻³, and the carbon atom concentration [C] was 5×10¹⁵ cm⁻³. Table I summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (20−2−1) in Example 2, substantially the same results were obtained even in the case that at least part of the plane orientations were (−202−1) (which is crystal-geometrically equivalent with (20−2−1)).

The GaN crystal produced in Example 2 had a lower formation of cracks than the GaN crystal produced in Example 1.

Example 3

First, with reference to FIG. 3A, both major surfaces, a (0001) plane and a (000−1) plane, of the GaN bulk crystal (a Group III nitride bulk crystal 1) were ground and polished to an average roughness Ra of 5 nm.

With reference to FIG. 3A, the GaN bulk crystal (the Group III nitride bulk crystal 1) in which the average roughness Ra of each of the major surfaces was 5 nm was cut perpendicularly to the <22−41> direction into a plurality of GaN crystal substrates (Group III nitride crystal substrates 10 p and 10 q). The GaN crystal substrates had a width S of 3.2 mm, a length L in the range of 20 to 50 mm, and a thickness T of 1 mm and had a {22−41} major surface. Four planes of each of the GaN crystal substrates not subjected to grinding and polishing were ground and polished to an average roughness Ra of 5 nm. Thus, a plurality of GaN crystal substrates were prepared in which the average roughness Ra of the {22−41} major surface was 5 nm. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {22−41}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {22−41}.

With reference to FIG. 3B, the plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (22−41) major surfaces 10 pm and 10 qm of the GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) were parallel to each other and each [0001] direction of the GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) coincided with each other. Also with reference to FIG. 3C, each of contact surfaces 10 pt and 10 qt of the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

With reference to FIG. 3C, the (22−41) major surfaces 10 pm and 10 qm of the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) arranged in the quartz crystal growth container were treated in the same way as in Example 1. A GaN crystal (a Group III nitride crystal 20) was then grown on the major surfaces 10 pm and 10 qm by the same growth method at the same growth temperature for the same growth time as in Example 1.

The GaN crystal (the Group III nitride crystal 20) had a thickness of 3.0 mm, and the crystal growth rate was 75 μm/h. With reference to the right side of the central portion in FIG. 3C, the GaN crystal (the Group III nitride crystal 20) had a (22−41) major surface 20 m in a region-on-substrate-interface 20 t and a region-on-substrate 20 s. A plurality of facets 20 mf on the (22−41) major surface 20 m formed depressions 20 v. The crystallinity of the GaN crystal (the Group III nitride crystal 20) was determined by the X-ray rocking curve measurement of the (22−41) plane. In the region-on-substrate 20 s, an unsplit diffraction peak having a full width at half maximum of 120 arcsec was observed. In the region-on-substrate-interface 20 t having a width ΔW of 300 μm, a split diffraction peak having a full width at half maximum of 220 arcsec was observed.

The (22−41) major surface 20 m of the GaN crystal had a threading dislocation density of 3×10⁷ cm⁻² in the region-on-substrate 20 s and 7×10⁷ cm⁻² in the region-on-substrate-interface 20 t. The planar defect density in the {0001} plane of the GaN crystal was determined to be 8.6 cm⁻¹ by cathodoluminescence (CL) of a cross section of the GaN crystal perpendicular to the <10−10> direction. The GaN crystal had a carrier concentration of 2×10¹⁸ cm⁻³ as calculated from the Hall measurement. The concentrations of the main impurity atoms of the GaN crystal were measured by secondary ion mass spectrometry (SIMS)) as follows: the oxygen atom concentration [O] was 2×10¹⁸ cm⁻³, the silicon atom concentration [Si] was 9×10¹⁷ cm⁻³, the hydrogen atom concentration [H] was 4×10¹⁶ cm⁻³, and the carbon atom concentration [C] was 5×10¹⁵ cm⁻³. Table I summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (22−41) in Example 3, substantially the same results were obtained even in the case that at least part of the plane orientations were (−4221) (which is crystal-geometrically equivalent with (22−41)).

Example 4

First, with reference to FIG. 4A, both major surfaces, a (0001) plane and a (000-1) plane, of the GaN bulk crystal (a Group III nitride bulk crystal 1) were ground and polished to an average roughness Ra of 5 nm.

With reference to FIG. 4A, the GaN bulk crystal (the Group III nitride bulk crystal 1) in which the average roughness Ra of each of the major surfaces was 5 nm was cut perpendicularly to the <22−4−1> direction into a plurality of GaN crystal substrates (Group III nitride crystal substrates 10 p and 10 q). The GaN crystal substrates had a width S of 3.2 mm, a length L in the range of 20 to 50 mm, and a thickness T of 1 mm and had a {22−4−1} major surface. Four planes of each of the GaN crystal substrates not subjected to grinding and polishing were ground and polished to an average roughness Ra of 5 nm. Thus, a plurality of GaN crystal substrates were prepared in which the average roughness Ra of the {22−4−1} major surface was 5 nm. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {22−4−1}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {22−4−1}.

With reference to FIG. 4B, the plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (22−4−1) major surfaces 10 pm and 10 qm of the GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) were parallel to each other and each [0001] direction of the GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) coincided with each other. Also with reference to FIG. 4C, each of contact surfaces 10 pt and 10 qt of the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

With reference to FIG. 4C, the (22−4−1) major surfaces 10 pm and 10 qm of the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) arranged in the quartz crystal growth container were treated in the same way as in Example 1. A GaN crystal (a Group III nitride crystal 20) was then grown on the major surfaces 10 pm and 10 qm by the same growth method at the same growth temperature for the same growth time as in Example 1.

The GaN crystal (the Group III nitride crystal 20) had a thickness of 4.0 mm, and the crystal growth rate was 100 μm/h. With reference to the right side of the central portion in FIG. 4C, the GaN crystal (the Group III nitride crystal 20) had a (22−4−1) major surface 20 m in a region-on-substrate-interface 20 t and a region-on-substrate 20 s. A plurality of facets 20 mf on the (22−4−1) major surface 20 m formed depressions 20 v. The crystallinity of the GaN crystal (the Group III nitride crystal 20) was determined by the X-ray rocking curve measurement of the (22−4−1) plane. In the region-on-substrate 20 s, an unsplit diffraction peak having a full width at half maximum of 140 arcsec was observed. In the region-on-substrate-interface 20 t having a width ΔW of 500 μm, a split diffraction peak having a full width at half maximum of 200 arcsec was observed.

The (22−4−1) major surface 20 m of the GaN crystal had a threading dislocation density of 3×10⁷ cm⁻² in the region-on-substrate 20 s and 7×10⁷ cm⁻² in the region-on-substrate-interface 20 t. The planar defect density in the {0001} plane of the GaN crystal was determined to be 7.9 cm⁻¹ by cathodoluminescence (CL) of a cross section of the GaN crystal perpendicular to the <10−10> direction. The GaN crystal had a carrier concentration of 2×10¹⁸ cm⁻³ as calculated from the Hall measurement. The concentrations of the main impurity atoms of the GaN crystal were measured by secondary ion mass spectrometry (SIMS)) as follows: the oxygen atom concentration [O] was 2×10¹⁸ cm⁻³, the silicon atom concentration [Si] was 9×10¹⁷ cm⁻³, the hydrogen atom concentration [H] was 4×10¹⁶ cm⁻³, and the carbon atom concentration [C] was 5×10¹⁵ cm⁻³. Table I summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (22−4−1) in Example 4, substantially the same results were obtained even in the case that at least part of the plane orientations were (−422−1) (which is crystal-geometrically equivalent with (22−4−1)).

TABLE I Example1 Example2 Example3 Example4 Group III Type of substrate GaN GaN GaN GaN nitride Plane orientation of main plane (20-21) (20-2-1) (22-41) (22-4-1) crystal Surface roughness Ra of main plane (mm)  5  5  5  5 substrate Surface roughness Ra of adjacent plane (mm)  5  5  5  5 Group III Type of crystal GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020  1020  1020  1020  Crystal growth rate (μm/hr)  60 80  75 100 Plane orientation of main plane (20-21) (20-2-1) (22-41) (22-4-1) Presence of depression in main plane No No Yes Yes Full width at half maximum Region-on-substrate 100 90 120 140 of X-ray diffraction peak Region-on-substrate- 300 360  220 200 (arcsec) interface Threading dislocation Region-on-substrate 1 × 10⁷  1 × 10⁷  3 × 10⁷  3 × 10⁷  density of main plane Region-on-substrate- 3 × 10⁷  4 × 10⁷  7 × 10⁷  7 × 10⁷  (cm⁻²) interface Planar defect density (cm⁻¹)    8.3   6.1    8.6    7.9 Carrier concentration (cm⁻³) 5 × 10¹⁸ 1 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ Main impurity atoms [O](cm⁻³) 5 × 10¹⁸ 9 × 10¹⁷ 2 × 10¹⁸ 2 × 10¹⁸ [Si](cm⁻³) 1 × 10¹⁸ 1 × 10¹⁸ 9 × 10¹⁷ 9 × 10¹⁷ [H](cm⁻³) 4 × 10¹⁶ 4 × 10¹⁶ 4 × 10¹⁶ 4 × 10¹⁶ [C](cm⁻³) 5 × 10¹⁵ 5 × 10¹⁵ 5 × 10¹⁵ 5 × 10¹⁵

As is clear from Table I, a high-crystallinity Group III nitride crystal having a major surface with a plane orientation other than {0001} can be grown at a high crystal growth rate by growing the Group III nitride crystal on a plurality of Group III nitride crystal substrates 10 p having the major surfaces 10 pm and 10 qm with a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}.

Comparative Example 1

A plurality of GaN crystal substrates (Group III nitride crystal substrates) in which a {1−100} major surface had an average roughness Ra of 5 nm were produced in the same way as in Example 1 except that the GaN bulk crystal (Group III nitride bulk crystal) was cut along a plurality of planes perpendicular to the <1−100> direction. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {1−100}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {1−100}. The off-angle was determined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (1−100) major surfaces of the GaN crystal substrates (Group III nitride crystal substrates) were parallel to each other and each direction of the GaN crystal substrates (Group III nitride crystal substrates) coincided with each other. Each of the contact surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (1−100) major surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) arranged in the quartz crystal growth container were treated in the same way as in Example 1. A GaN crystal (Group III nitride crystal) was then grown on the major surfaces by the same growth method at the same growth temperature for the same growth time as in Example 1.

The GaN crystal (Group III nitride crystal) had a thickness of 0.8 mm, and the crystal growth rate was 20 μm/h. The GaN crystal (Group III nitride crystal) had no abnormal crystal growth also in the region-on-substrate-interface 20 t and had a (1−100) major surface. The crystallinity of the GaN crystal (Group III nitride crystal) was determined by the X-ray rocking curve measurement of the (1−100) plane. In the region-on-substrate of the GaN crystal, an unsplit diffraction peak having a full width at half maximum of 100 arcsec was observed. In the region-on-substrate-interface having a width ΔW of 300 μm, a split diffraction peak having a full width at half maximum of 300 arcsec was observed.

The (1−100) major surface of the GaN crystal had a threading dislocation density of 1×10⁷ cm⁻² in the region-on-substrate and 3×10⁷ cm⁻² in the region-on-substrate-interface. The GaN crystal had a carrier concentration of 5×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystal were oxygen (O) atoms and silicon (Si) atoms. Table II summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (1−100) in Comparative Example 1, substantially the same results were obtained even in the case that at least part of the plane orientations were (−1100) (which is crystal-geometrically equivalent with (1−100)).

Comparative Example 2

A plurality of GaN crystal substrates (Group III nitride crystal substrates) in which a {11−20} major surface had an average roughness Ra of 5 nm were produced in the same way as in Example 1 except that the GaN bulk crystal (Group III nitride bulk crystal) was cut along a plurality of planes perpendicular to the <11−20> direction. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {11−20}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {11−20}. The off-angle was determined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (11−20) major surfaces of the GaN crystal substrates (Group III nitride crystal substrates) were parallel to each other and each direction of the GaN crystal substrates (Group III nitride crystal substrates) coincided with each other. Each of the contact surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (11−20) major surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) arranged in the quartz crystal growth container were treated in the same way as in Example 1. A GaN crystal (Group III nitride crystal) was then grown on the major surfaces by the same growth method at the same growth temperature for the same growth time as in Example 1.

The GaN crystal (Group III nitride crystal) had a thickness of 0.8 mm, and the crystal growth rate was 20 μm/h. The GaN crystal (Group III nitride crystal) had no abnormal crystal growth also in the region-on-substrate-interface 20 t and had a (11−20) major surface. The crystallinity of the GaN crystal (the Group III nitride crystal) was determined by the X-ray rocking curve measurement of the (11−20) plane. In the region-on-substrate of the GaN crystal, an unsplit diffraction peak having a full width at half maximum of 250 arcsec was observed. In the region-on-substrate-interface having a width ΔW of 300 μm, a split diffraction peak having a full width at half maximum of 620 arcsec was observed.

The (11−20) major surface of the GaN crystal had a threading dislocation density of 1×10⁷ cm⁻² in the region-on-substrate and 8×10⁷ cm⁻² in the region-on-substrate-interface. The GaN crystal had a carrier concentration of 5×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystal were oxygen (O) atoms and silicon (Si) atoms. Table II summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (11−20) in Comparative Example 2, substantially the same results were obtained even in the case that at least part of the plane orientations were (−1−120) (which is crystal-geometrically equivalent with (11−20)).

Comparative Example 3

A plurality of GaN crystal substrates (Group III nitride crystal substrates) in which a {1−102} major surface had an average roughness Ra of 5 nm were produced in the same way as in Example 1 except that the GaN bulk crystal (Group III nitride bulk crystal) was cut along a plurality of planes perpendicular to the <1−102> direction. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {1−102}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {1−102}. The off-angle was determined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (1−102) major surfaces of the GaN crystal substrates (Group III nitride crystal substrates) were parallel to each other and each direction of the GaN crystal substrates (Group III nitride crystal substrates) coincided with each other. Each of the contact surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (1−102) major surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) arranged in the quartz crystal growth container were treated in the same way as in Example 1. A GaN crystal (Group III nitride crystal) was then grown on the major surfaces by the same growth method at the same growth temperature for the same growth time as in Example 1.

The GaN crystal (Group III nitride crystal) had a thickness of 0.8 mm, and the crystal growth rate was 20 μm/h. The GaN crystal (Group III nitride crystal) had no abnormal crystal growth also in the region-on-substrate-interface 20 t and had a (1−102) major surface. The crystallinity of the GaN crystal (the Group III nitride crystal) was determined by the X-ray rocking curve measurement of the (1−102) plane. In the region-on-substrate of the GaN crystal, an unsplit diffraction peak having a full width at half maximum of 120 arcsec was observed. In the region-on-substrate-interface having a width ΔW of 300 μm, a split diffraction peak having a full width at half maximum of 480 arcsec was observed.

The (1−102) major surface of the GaN crystal had a threading dislocation density of 1×10⁷ cm⁻² in the region-on-substrate and 6×10⁷ cm⁻² in the region-on-substrate-interface. The GaN crystal had a carrier concentration of 5×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystal were oxygen (O) atoms and silicon (Si) atoms. Table II summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (1−102) in Comparative Example 3, substantially the same results were obtained even in the case that at least part of the plane orientations were (−1102) (which is crystal-geometrically equivalent with (1−102)).

Comparative Example 4

A plurality of GaN crystal substrates (Group III nitride crystal substrates) in which a {11−22} major surface had an average roughness Ra of 5 nm were produced in the same way as in Example 1 except that the GaN bulk crystal (Group III nitride bulk crystal) was cut along a plurality of planes perpendicular to the <11−22> direction. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {11−22}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {11−22}. The off-angle was determined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (11−22) major surfaces of the GaN crystal substrates (Group III nitride crystal substrates) were parallel to each other and each direction of the GaN crystal substrates (Group III nitride crystal substrates) coincided with each other. Each of the contact surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (11−22) major surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) arranged in the quartz crystal growth container were treated in the same way as in Example 1. A GaN crystal (Group III nitride crystal) was then grown on the major surfaces by the same growth method at the same growth temperature for the same growth time as in Example 1.

The GaN crystal (Group III nitride crystal) had a thickness of 0.8 mm, and the crystal growth rate was 20 μm/h. The GaN crystal (Group III nitride crystal) had no abnormal crystal growth also in the region-on-substrate-interface 20 t and had a (11−22) major surface. The crystallinity of the GaN crystal (Group III nitride crystal) was determined by the X-ray rocking curve measurement of the (11−22) plane. In the region-on-substrate of the GaN crystal, an unsplit diffraction peak having a full width at half maximum of 90 arcsec was observed. In the region-on-substrate-interface having a width ΔW of 500 μm, a split diffraction peak having a full width at half maximum of 380 arcsec was observed.

The (11−22) major surface of the GaN crystal had a threading dislocation density of 1×10⁷ cm⁻² in the region-on-substrate and 4×10⁷ cm⁻² in the region-on-substrate-interface. The GaN crystal had a carrier concentration of 5×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystal were oxygen (O) atoms and silicon (Si) atoms. Table II summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (11−22) in Comparative Example 4, substantially the same results were obtained even in the case that at least part of the plane orientations were (−1−122) (which is crystal-geometrically equivalent with (11−22)).

Comparative Example 5

A plurality of GaN crystal substrates (Group III nitride crystal substrates) in which a {12−30} major surface had an average roughness Ra of 5 nm were produced in the same way as in Example 1 except that the GaN bulk crystal (Group III nitride bulk crystal) was cut along a plurality of planes perpendicular to the <12−30> direction. In some of the GaN crystal substrates, the plane orientation of the major surface did not precisely coincide with {12−30}. In all such GaN crystal substrates, however, the plane orientation of the major surface had an off-angle of five degrees or less with respect to {12−30}. The off-angle was determined by an X-ray diffraction method.

The plurality of GaN crystal substrates were transversely arranged adjacent to each other in a quartz crystal growth container such that (12−30) major surfaces of the GaN crystal substrates (Group III nitride crystal substrates) were parallel to each other and each direction of the GaN crystal substrates (Group III nitride crystal substrates) coincided with each other. Each of the contact surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) had an average roughness Ra of 5 nm. A circle inscribed in the plurality of GaN crystal substrates (the Group III nitride crystal substrates 10 p and 10 q) thus arranged had a diameter of 50 mm.

The (12−30) major surfaces of the plurality of GaN crystal substrates (Group III nitride crystal substrates) arranged in the quartz crystal growth container were treated in the same way as in Example 1. A GaN crystal (Group III nitride crystal) was then grown on the major surfaces by the same growth method at the same growth temperature for the same growth time as in Example 1.

The GaN crystal (Group III nitride crystal) had a thickness of 0.8 mm, and the crystal growth rate was 20 μm/h. The GaN crystal (Group III nitride crystal) had no abnormal crystal growth also in the region-on-substrate-interface 20 t and had a (12−30) major surface. The crystallinity of the GaN crystal (Group III nitride crystal) was determined by the X-ray rocking curve measurement of the (12−30) plane. In the region-on-substrate of the GaN crystal, an unsplit diffraction peak having a full width at half maximum of 280 arcsec was observed. In the region-on-substrate-interface having a width ΔW of 500 μm, a split diffraction peak having a full width at half maximum of 660 arcsec was observed.

The (12−30) major surface of the GaN crystal had a threading dislocation density of 1×10⁷ cm⁻² in the region-on-substrate and 7×10⁷ cm⁻² in the region-on-substrate-interface. The GaN crystal had a carrier concentration of 4×10¹⁸ cm⁻³. The main impurity atoms of the GaN crystal were oxygen (O) atoms and silicon (Si) atoms. Table II summarizes the results.

Although all the plane orientations of the major surfaces of the plurality of GaN crystal substrates on which a GaN crystal was grown were (12−30) in Comparative Example 5, substantially the same results were obtained even in the case that at least part of the plane orientations were (−1−230) (which is crystal-geometrically equivalent with (12−30)).

TABLE II Comparative Comparative Comparative Comparative Comparative Example1 Example2 Example3 Example4 Example3 Group III Type of substrate GaN GaN GaN GaN GaN nitride Plane orientation of main plane (1-100) (11-20) (1-102) (11-22) (12-30) crystal Surface roughness Ra of main plane (mm)  5  5  5  5  5 substrate Surface roughness Ra of adjacent plane (mm)  5  5  5  5  5 Group III Type of crystal GaN GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020  1020  1020  1020  1020  Crystal growth rate (μm/hr)  20  20  20 20  20 Plane orientation of main plane (1-100) (11-20) (1-102) (11-22) (12-30) Presence of depression in main plane No Yes No No Yes Full width at half maximum Region-on-substrate 100 250 120 90 280 of X-ray diffraction peak Region-on- 300 620 480 380  660 (arcsec) substrate-interface Threading dislocation Region-on-substrate 1 × 10⁷ 1 × 10⁷ 1 × 10⁷ 1 × 10⁷ 1 × 10⁷ density of main plane Region-on- 3 × 10⁷ 8 × 10⁷ 6 × 10⁷ 4 × 10⁷ 7 × 10⁷ (cm⁻²) substrate-interface Carrier concentration (cm⁻³)  5 × 10¹⁸  5 × 10¹⁸  5 × 10¹⁸  5 × 10¹⁸  4 × 10¹⁸ Main impurity atoms O, Si O, Si O, Si O, Si O, Si

With reference to Tables I and II, the use of a plurality of Group III nitride crystal substrates having a major surface with a plane orientation of {1−100}, {11−20}, {1−102}, {11−22}, or {12−30} also yielded a high-crystallinity Group III nitride crystal having a major surface with a plane orientation other than {0001} but resulted in a lower crystal growth rate than the use of a plurality of Group III nitride crystal substrates having a major surface with a plane orientation of {20−21}, {20−2−1}, {22−41}, or {22−4−1}.

Examples 5 Through 8

In Example 5, a GaN crystal (Group III nitride crystal) was grown in the same way as in Example 1 except that the inner wall of the quartz crystal growth container was covered with a BN plate and the crystal growth rate was 70 μm/h. In Example 6, a GaN crystal (Group III nitride crystal) was grown in the same way as in Example 5 except that the crystal growth rate was 80 μm/h. In Example 7, a GaN crystal (Group III nitride crystal) was grown in the same way as in Example 5 except that O₂ gas diluted with N₂ gas, SiCl₄ gas, H₂ gas, and CH₄ gas were used to add high concentrations of oxygen atoms, silicon atoms, hydrogen atoms, and carbon atoms to the GaN crystal. In Example 8, a GaN crystal (Group III nitride crystal) was grown in the same way as in Example 7 except that the crystal growth rate was 80 μm/h. Table III summarizes the results.

Examples 9 Through 12

In Example 9, a GaN crystal (Group III nitride crystal) was grown in the same way as in Example 2 except that the inner wall of the quartz crystal growth container was covered with a BN plate. In Example 10, a GaN crystal (Group III nitride crystal) was grown in the same way as in Example 9 except that the crystal growth rate was 90 μm/h. In Example 11, a GaN crystal (Group III nitride crystal) was grown in the same way as in Example 9 except that O₂ gas diluted with N₂ gas, SiCl₄ gas, H₂ gas, and CH₄ gas were used to add high concentrations of oxygen atoms, silicon atoms, hydrogen atoms, and carbon atoms to the GaN crystal. In Example 12, a GaN crystal (Group III nitride crystal) was grown in the same way as in Example 11 except that the crystal growth rate was 90 μm/h. Table III summarizes the results.

TABLE III Example 5 Example 6 Example 7 Example 8 Group III Type of substrate GaN GaN GaN GaN nitride Plane orientation of main plane (20-21) (20-21) (20-21) (20-21) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 Crystal growth rate (μm/hr) 70 80 70 80 Plane orientation of main plane (20-21) (20-21) (20-21) (20-21) Presence of depression in main plane No Yes No Yes Full width at half maximum of Region-on-substrate 110 160 110 170 X-ray diffraction peak Region-on-substrate- 300 390 300 390 (arcsec) interface Threading dislocation density Region-on-substrate 1 × 10⁷  5 × 10⁷  2 × 10⁷  5 × 10⁷  of main plane (cm⁻²) Region-on-substrate- 2 × 10⁷  7 × 10⁷  4 × 10⁷  8 × 10⁷  interface Planar defect density (cm⁻¹) 8.2 35 7.8 49 Carrier concentration (cm⁻³) ~1 × 10¹⁶  ~1 × 10¹⁶  4 × 10¹⁹ 4 × 10¹⁹ Main impurity atoms [O](cm⁻³) 5 × 10¹⁵ 5 × 10¹⁵ 5 × 10¹⁹ 5 × 10¹⁹ [Si](cm⁻³) 3 × 10¹⁴ 3 × 10¹⁴ 6 × 10¹⁸ 6 × 10¹⁸ [H](cm⁻³) 4 × 10¹⁶ 4 × 10¹⁶ 3 × 10¹⁸ 3 × 10¹⁸ [C](cm⁻³) 5 × 10¹⁵ 5 × 10¹⁵ 2 × 10¹⁸ 2 × 10¹⁸ Example 9 Example 10 Example 11 Example 12 Group III Type of substrate GaN GaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 Crystal growth rate (μm/hr) 80 90 80 90 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane No Yes No Yes Full width at half maximum of Region-on-substrate 80 160 90 165 X-ray diffraction peak Region-on-substrate- 290 395 290 380 (arcsec) interface Threading dislocation density Region-on-substrate 1 × 10⁷  6 × 10⁷  2 × 10⁷  5 × 10⁷  of main plane (cm⁻²) Region-on-substrate- 2 × 10⁷  7 × 10⁷  3 × 10⁷  8 × 10⁷  interface Planar defect density (cm⁻¹) 7.4 37 6.5 51 Carrier concentration (cm⁻³) ~1 × 10¹⁶  ~1 × 10¹⁶  4 × 10¹⁹ 4 × 10¹⁹ Main impurity atoms [O](cm⁻³) 5 × 10¹⁵ 5 × 10¹⁵ 5 × 10¹⁹ 5 × 10¹⁹ [Si](cm⁻³) 3 × 10¹⁴ 3 × 10¹⁴ 6 × 10¹⁸ 6 × 10¹⁸ [H](cm⁻³) 4 × 10¹⁶ 4 × 10¹⁶ 3 × 10¹⁸ 3 × 10¹⁸ [C](cm⁻³) 5 × 10¹⁵ 5 × 10¹⁵ 2 × 10¹⁸ 2 × 10¹⁸

Table III shows the following results in Examples 5 to 8, in which a GaN crystal was grown on a GaN crystal substrate having a major surface with a plane orientation with an off-angle of five degrees or less with respect to {20−21}. In the grown GaN crystal having an oxygen atom concentration below 1×10¹⁶ cm⁻³, a silicon atom concentration below 6×10¹⁴ cm⁻³, a hydrogen atom concentration below 6×10¹⁶ cm⁻³, and a carbon atom concentration below 1×10¹⁶ cm⁻³, the planar defect density in the {0001} in-plane of the GaN crystal was as low as 8.2 cm⁻¹ at a crystal growth rate of 70 μm/h (less than 80 μm/h) (Example 5) and as high as 35 cm⁻¹ at a crystal growth rate of 80 μm/h (80 μm/h or more) (Example 6). Likewise, in the grown GaN crystal having an oxygen atom concentration above 4×10¹⁹ cm⁻³, a silicon atom concentration above 5×10¹⁸ cm⁻³, a hydrogen atom concentration above 1×10¹⁸ cm⁻³, and a carbon atom concentration above 1×10¹⁸ cm⁻³, the planar defect density in the {0001} plane of the GaN crystal was as low as 7.2 cm⁻¹ at a crystal growth rate of 70 μm/h (less than 80 μm/h) (Example 7) and as high as 49 cm⁻¹ at a crystal growth rate of 80 μm/h (80 μm/h or more) (Example 8).

Table III also shows the following results in Examples 9 to 12, in which a GaN crystal was grown on a GaN crystal substrate having a major surface with a plane orientation with an off-angle of five degrees or less with respect to {20−2−1}. In the grown GaN crystal having an oxygen atom concentration below 1×10¹⁶ cm⁻³, a silicon atom concentration below 6×10¹⁴ cm⁻³, a hydrogen atom concentration below 6×10¹⁶ cm⁻³, and a carbon atom concentration below 1×10¹⁶ cm⁻³, the planar defect density in the {0001} plane of the GaN crystal was as low as 7.4 cm⁻¹ at a crystal growth rate of 80 μm/h (less than 90 μm/h) (Example 9) and as high as 37 cm⁻¹ at a crystal growth rate of 90 μm/h (90 μm/h or more) (Example 10). Likewise, in the grown GaN crystal having an oxygen atom concentration above 4×10¹⁹ cm⁻³, a silicon atom concentration above 5×10¹⁸ cm⁻³, a hydrogen atom concentration above 1×10¹⁸ cm⁻³, and a carbon atom concentration above 1×10¹⁸ cm⁻³, the planar defect density in the {0001} plane of the GaN crystal was as low as 6.5 cm⁻¹ at a crystal growth rate of 80 μm/h (less than 90 μm/h) (Example 11) and as high as 51 cm⁻¹ at a crystal growth rate of 90 μm/h (90 μm/h or more) (Example 12).

Examples 13 Through 20

In Examples 13 to 19, a GaN crystal was grown in the same way as in Example 12 except that the concentration of oxygen atoms added to the GaN crystal (Group III nitride crystal) grown was altered. In Example 20, a GaN crystal was grown in the same way as in Example 16 except that the crystal growth rate was 250 μm/h. Table IV summarizes the results.

TABLE IV Example 13 Example 14 Example 15 Example 16 Group III Type of substrate GaN GaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 90 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes Yes Full width at half Region-on-substrate 110 115 110 110 maximum of X- Region-on-substrate-interface 365 350 360 365 ray diffraction peak (arcsec) Threading Region-on-substrate 2 × 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  dislocation Region-on-substrate-interface 4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  density of main plane (cm⁻²) Planar defect density (cm⁻¹) 25 14.8 13.5 12.6 Carrier concentration (cm⁻³) 5 × 10¹⁸ 5 × 10¹⁸ 4 × 10¹⁸ 5 × 10¹⁸ Main impurity [O](cm⁻³) 9 × 10¹⁵ 2 × 10¹⁶ 5 × 10¹⁶ 2 × 10¹⁸ atoms [Si](cm⁻³) 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ [H](cm⁻³) 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ [C](cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ Example 17 Example 18 Example 19 Example 20 Group III Type of substrate GaN GaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 250 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes Yes Full width at half Region-on-substrate 120 125 110 95 maximum of X- Region-on-substrate-interface 370 365 365 280 ray diffraction peak (arcsec) Threading Region-on-substrate 1 × 10⁷  2 × 10⁷  4 × 10⁷  5 × 10⁶  dislocation Region-on-substrate-interface 4 × 10⁷  4 × 10⁷  5 × 10⁷  9 × 10⁶  density of main plane (cm⁻²) Planar defect density (cm⁻¹) 14.6 17.5 34 18.7 Carrier concentration (cm⁻³) 1 × 10¹⁹ 4 × 10¹⁹ 6 × 10¹⁹ 6 × 10¹⁸ Main impurity [O](cm⁻³) 9 × 10¹⁸ 2 × 10¹⁹ 6 × 10¹⁹ 2 × 10¹⁸ atoms [Si](cm⁻³) 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ [H](cm⁻³) 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ [C](cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸

With reference to Table IV, the planar defect density in the {0001} plane of a GaN crystal grown on a GaN crystal substrate having a major surface with a plane orientation with an off-angle of five degrees or less with respect to {20−2−1} was reduced even at a crystal growth rate of 90 μm/h (90 μm/h or more) when the concentration of oxygen atom, which was one of the impurity atoms in the GaN crystal, was preferably 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less (Examples 14 to 18), more preferably 5×10¹⁶ cm⁻³ or more and 1×10¹⁹ cm⁻³ or less (Examples 15 to 17), still more preferably 1×10¹⁷ cm⁻³ or more and 8×10¹⁸ cm⁻³ or less (Example 16). An oxygen atom concentration of the GaN crystal of 1×10¹⁷ cm⁻³ or more and 8×10¹⁸ cm⁻³ or less resulted in a low planar defect density in the {0001} plane of the GaN crystal even when the crystal growth rate was increased to 250 μm/h.

Examples 21 Through 27

In Examples 21 to 27, a GaN crystal was grown in the same way as in Example 12 except that the concentration of silicon atoms added to the GaN crystal (Group III nitride crystal) grown was altered. Table V summarizes the results.

TABLE V Example Example Example Example Example 21 Example 22 Example 23 24 25 26 27 Group III Type of substrate GaN GaN GaN GaN GaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 90 90 90 90 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes Yes Yes Yes Yes Full width at half Region-on-substrate 120 120 110 120 120 118 140 maximum of X-ray Region-on-substrate- 380 376 376 376 365 376 376 diffraction peak interface (arcsec) Threading dislocation Region-on-substrate 3 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  4 × 10⁷  density of main plane Region-on-substrate- 5 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  (cm⁻²) interface Planar defect density (cm⁻¹) 23.9 18.4 16.3 15.3 17.1 18.4 32.3 Carrier concentration (cm⁻³) 3 × 10¹⁹ 3 × 10¹⁹ 3 × 10¹⁹ 3 × 10¹⁹ 3 × 10¹⁹ 3 × 10¹⁹ 4 × 10¹⁹ Main impurity atoms [O](cm⁻³) 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ [Si](cm⁻³) 5 × 10¹⁴ 7 × 10¹⁴ 2 × 10¹⁵ 1 × 10¹⁸ 2 × 10¹⁸ 4 × 10¹⁸ 6 × 10¹⁸ [H](cm⁻³) 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ [C](cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸

With reference to Table V, the planar defect density in the {0001} plane of a GaN crystal grown on a GaN crystal substrate having a major surface with a plane orientation with an off-angle of five degrees or less with respect to {20−2−1} was reduced even at a crystal growth rate of 90 μm/h (90 μm/h or more) when the concentration of silicon atom, which was one of the impurity atoms in the GaN crystal, was preferably 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less (Examples 22 to 26), more preferably 1×10¹⁵ cm⁻³ or more and 3×10¹⁸ cm⁻³ or less (Examples 23 to 25), still more preferably 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less (Example 24).

Examples 28 Through 34

In Examples 28 to 34, a GaN crystal was grown in the same way as in Example 12 except that the concentration of hydrogen atoms added to the GaN crystal (Group III nitride crystal) grown was altered. Table VI summarizes the results.

TABLE VI Example Example Example Example Example 28 Example 29 Example 30 31 32 33 34 Group III Type of substrate GaN GaN GaN GaN GaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 90 90 90 90 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes Yes Yes Yes Yes Full width at half Region-on-substrate 120 122 125 120 120 115 135 maximum of X-ray Region-on-substrate- 375 370 372 370 368 365 384 diffraction peak interface (arcsec) Threading dislocation Region-on-substrate 2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  2 × 10⁷  density of main plane Region-on-substrate- 5 × 10⁷  5 × 10⁷  5 × 10⁷  5 × 10⁷  5 × 10⁷  5 × 10⁷  5 × 10⁷  (cm⁻²) interface Planar defect density (cm⁻¹) 22.3 17.6 16.1 16.1 16.3 17.5 28.1 Carrier concentration (cm⁻³) 4 × 10¹⁹ 4 × 10¹⁹ 4 × 10¹⁹ 4 × 10¹⁹ 4 × 10¹⁹ 4 × 10¹⁹ 4 × 10¹⁹ Main impurity atoms [O](cm⁻³) 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ [Si](cm⁻³) 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ [H](cm⁻³) 5 × 10¹⁶ 7 × 10¹⁶ 1 × 10¹⁷ 7 × 10¹⁷ 8 × 10¹⁷ 1 × 10¹⁸ 2 × 10¹⁸ [C](cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸

With reference to Table VI, the planar defect density in the {0001} plane of a GaN crystal grown on a GaN crystal substrate having a major surface with a plane orientation with an off-angle of five degrees or less with respect to {20−2−1} was reduced even at a crystal growth rate of 90 μm/h (90 μm/h or more) when the concentration of hydrogen atom, which was one of the impurity atoms in the GaN crystal, was preferably 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less (Examples 29 to 33), more preferably 1×10¹⁷ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less (Examples 30 to 32), still more preferably 2×10¹⁷ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less (Example 31).

Examples 35 Through 41

In Examples 35 to 41, a GaN crystal was grown in the same way as in Example 12 except that the concentration of carbon atoms added to the GaN crystal (Group III nitride crystal) grown was altered. Table VII summarizes the results.

TABLE VII Example Example Example Example Example 35 Example 36 Example 37 38 39 40 41 Group III Type of substrate GaN GaN GaN GaN GaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 90 90 90 90 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes Yes Yes Yes Yes Full width at half Region-on-substrate 125 120 110 110 115 120 125 maximum of X-ray Region-on-substrate- 378 375 375 375 370 370 378 diffraction peak interface (arcsec) Threading dislocation Region-on-substrate 1 × 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  1 × 10⁷  2 × 10⁷  density of main plane Region-on-substrate- 4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  4 × 10⁷  (cm⁻²) interface Planar defect density (cm⁻¹) 25.5 19.7 17.4 16 17.8 18.6 31.1 Carrier concentration (cm⁻³) 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ Main impurity atoms [O](cm⁻³) 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ [Si](cm⁻³) 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ [H](cm⁻³) 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ 3 × 10¹⁸ [C](cm⁻³) 8 × 10¹⁵ 2 × 10¹⁶ 6 × 10¹⁶ 3 × 10¹⁷ 8 × 10¹⁷ 1 × 10¹⁸ 3 × 10¹⁸

With reference to Table VII, the planar defect density in the {0001} plane of a GaN crystal grown on a GaN crystal substrate having a major surface with a plane orientation with an off-angle of five degrees or less with respect to {20−2−1} was reduced even at a crystal growth rate of 90 μm/h (90 μm/h or more) when the concentration of carbon atom, which was one of the impurity atoms in the GaN crystal, was preferably 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less (Examples 36 to 40), more preferably 5×10¹⁶ cm⁻³ or more and 9×10¹⁷ cm⁻³ or less (Examples 37 to 39), still more preferably 9×10¹⁶ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less (Example 38).

Examples 42 Through 47

In Examples 42 to 47, a GaN crystal was grown in the same way as in Example 12 except that the concentration of an impurity atom added to the GaN crystal (Group III nitride crystal) grown was adjusted to satisfy two of the oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, the silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, the hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and the carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. Table VIII summarizes the results.

TABLE VIII Example 42 Example 43 Example 44 Example 45 Example 46 Example 47 Group III Type of substrate GaN GaN GaN GaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 90 90 90 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes Yes Yes Yes Full width at half maximum Region-on-substrate 90 88 95 84 80 80 of X-ray diffraction Region-on-substrate- 310 280 320 240 210 220 peak (arcsec) interface Threading dislocation Region-on-substrate 4 × 10⁶  4 × 10⁶  6 × 10⁶  3 × 10⁶  3 × 10⁶  3 × 10⁶  density of main plane Region-on-substrate- 9 × 10⁶  8 × 10⁶  1 × 10⁷  7 × 10⁶  7 × 10⁶  6 × 10⁶  (cm⁻²) interface Planar defect density (cm⁻¹) 6 7.3 6.7 10 9.6 11.8 Carrier concentration (cm⁻³) 1 × 10¹⁸ 4 × 10¹⁸ 6 × 10¹⁸ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ Main impurity atoms [O](cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 5 × 10¹⁹ 5 × 10¹⁹ 5 × 10¹⁹ [Si](cm⁻³) 1 × 10¹⁸ 6 × 10¹⁸ 6 × 10¹⁸ 1 × 10¹⁸ 1 × 10¹⁸ 6 × 10¹⁸ [H](cm⁻³) 3 × 10¹⁸ 7 × 10¹⁷ 3 × 10¹⁸ 7 × 10¹⁷ 3 × 10¹⁸ 7 × 10¹⁷ [C](cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 3 × 10¹⁷ 2 × 10¹⁸ 3 × 10¹⁷ 3 × 10¹⁷

With reference to Table VIII, the planar defect density in the {0001} plane of a GaN crystal grown on a GaN crystal substrate having a major surface with a plane orientation with an off-angle of five degrees or less with respect to {20−2−1} was greatly reduced even at a crystal growth rate of 90 μm/h (90 μm/h or more) when two of the impurity atom concentrations, that is, the oxygen atom concentration, the silicon atom concentration, the hydrogen atom concentration, and the carbon atom concentration, of the GaN crystal were in the predetermined range described above (Examples 42 to 47).

Examples 48 Through 51

In Examples 48 to 51, a GaN crystal was grown in the same way as in Example 12 except that the concentration of an impurity atom added to the GaN crystal (Group III nitride crystal) grown was adjusted to satisfy three of the oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, the silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, the hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and the carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. Table IX summarizes the results.

Examples 52 and 53

In Example 52, a GaN crystal was grown in the same way as in Example 12 except that the concentration of an impurity atom added to the GaN crystal (Group III nitride crystal) grown was adjusted to satisfy all (four) of the oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, the silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, the hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and the carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less. In Example 53, a GaN crystal was grown in the same way as in Example 52 except that the crystal growth rate was 250 μm/h. Table IX summarizes the results.

TABLE IX Example 48 Example 49 Example 50 Example 51 Example 52 Example 53 Group III Type of substrate GaN GaN GaN GaN GaN GaN nitride Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) crystal Surface roughness Ra of main plane (mm) 5 5 5 5 5 5 substrate Surface roughness Ra of adjacent plane (mm) 5 5 5 5 5 5 Group III Type of crystal GaN GaN GaN GaN GaN GaN nitride Crystal growth method HVPE HVPE HVPE HVPE HVPE HVPE crystal Crystal growth temperature (° C.) 1020 1020 1020 1020 1020 1020 Crystal growth rate (μm/hr) 90 90 90 90 90 250 Plane orientation of main plane (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) (20-2-1) Presence of depression in main plane Yes Yes Yes Yes Yes Yes Full width at half maximum Region-on-substrate 80 77 74 80 65 70 of X-ray diffraction peak Region-on-substrate- 160 135 120 190 80 95 (arcsec) interface Threading dislocation Region-on-substrate 8 × 10⁵  6 × 10⁵  6 × 10⁵  7 × 10⁵  2 × 10⁵  4 × 10⁵  density of main plane Region-on-substrate- 5 × 10⁶  3 × 10⁶  4 × 10⁶  6 × 10⁶  2 × 10⁶  3 × 10⁶  (cm⁻²) interface Planar defect density (cm⁻¹) 3.8 3.6 3.2 4.9 0.3 0.8 Carrier concentration (cm⁻³) 1 × 10¹⁸ 7 × 10¹⁸ 1 × 10¹⁸ 5 × 10¹⁹ 1 × 10¹⁸ 4 × 10¹⁸ Main impurity atoms [O](cm⁻³) 2 × 10¹⁸ 2 × 10¹⁸ 2 × 10¹⁸ 5 × 10¹⁹ 2 × 10¹⁸ 2 × 10¹⁸ [Si](cm⁻³) 1 × 10¹⁸ 6 × 10¹⁸ 1 × 10¹⁸ 1 × 10¹⁸ 1 × 10¹⁸ 1 × 10¹⁸ [H](cm⁻³) 7 × 10¹⁷ 7 × 10¹⁷ 3 × 10¹⁸ 7 × 10¹⁷ 7 × 10¹⁷ 7 × 10¹⁷ [C](cm⁻³) 2 × 10¹⁸ 3 × 10¹⁷ 3 × 10¹⁷ 3 × 10¹⁷ 3 × 10¹⁷ 3 × 10¹⁷

With reference to Table IX, the planar defect density in the {0001} plane of a GaN crystal grown on a GaN crystal substrate having a major surface with a plane orientation with an off-angle of five degrees or less with respect to {20−2−1} was more greatly reduced even at a crystal growth rate of 90 μm/h (90 μm/h or more) when three of the impurity atom concentrations, that is, the oxygen atom concentration, the silicon atom concentration, the hydrogen atom concentration, and the carbon atom concentration, of the GaN crystal were in the predetermined range described above (Examples 48 to 51). The planar defect density in the {0001} plane of the GaN crystal was still more greatly reduced when all (four) of the impurity atom concentrations, that is, the oxygen atom concentration, the silicon atom concentration, the hydrogen atom concentration, and the carbon atom concentration, of the GaN crystal were in the predetermined range described above (Example 52). Furthermore, the planar defect density in the {0001} plane of the GaN crystal was very low even at a crystal growth rate as high as 250 μm/h when all (four) of the impurity atom concentrations, that is, the oxygen atom concentration, the silicon atom concentration, the hydrogen atom concentration, and the carbon atom concentration, of the GaN crystal were in the predetermined range described above.

Examples 54 and 55

In Example 54, a GaN crystal was grown in the same way as in Example 52 except that the GaN crystal (Group III nitride crystal) prepared in Example 52 was cut along planes parallel to a major surface of a GaN crystal substrate (Group III nitride substrate), the major surfaces were ground and polished to produce a plurality of additional GaN crystal substrates (additional Group III nitride crystal substrates) having a thickness of 1 mm and an average roughness Ra of the major surface of 5 nm, a crystal was grown on the (20−21) major surface of the second additional GaN crystal substrate from the bottom, and the crystal growth rate was 140 μm/h. In Example 55, a GaN crystal was grown in the same way as in Example 52 except that the GaN crystal (Group III nitride crystal) prepared in Example 52 was cut along planes parallel to a major surface of a GaN crystal substrate (Group III nitride substrate), the major surfaces were ground and polished to produce a plurality of additional GaN crystal substrates (additional Group III nitride crystal substrates) having a thickness of 1 mm and an average roughness Ra of the major surface of 5 nm, a crystal was grown on the (20−21) major surface of the second additional GaN crystal substrate from the bottom, and the crystal growth rate was 150 μm/h. Table X summarizes the results.

TABLE X Example54 Example55 Group III Type of substrate Substrate obtained from GaN Substrate obtained from GaN nitride crystal prepared in Example 52 crystal prepared in Example 52 crystal (second from bottom) (second from bottom) substrate Plane orientation of main plane (20-2-1) (20-2-1) Surface roughness Ra of main plane (mm)  5  5 Surface roughness Ra of adjacent plane (mm)  5  5 Group III Type of crystal GaN GaN nitride Crystal growth method HVPE HVPE crystal Crystal growth temperature (° C.) 1020  1020  Crystal growth rate (μm/hr) 140  150  Plane orientation of main plane (20-2-1) (20-2-1) Presence of depression in main plane No Yes Full width at half maximum Region-on-substrate 65 70 of X-ray diffraction peak Region-on-substrate- 80 95 (arcsec) interface Threading dislocation Region-on-substrate 2 × 10⁵  4 × 10⁵  density of main plane Region-on-substrate- 2 × 10⁶  3 × 10⁶  (cm⁻²) interface Planar defect density (cm⁻¹)   0.3   0.3 Carrier concentration (cm⁻³) 4 × 10¹⁹ 1 × 10¹⁸ Main impurity atoms [O](cm⁻³) 5 × 10¹⁹ 2 × 10¹⁸ [Si](cm⁻³) 6 × 10¹⁸ 1 × 10¹⁸ [H](cm⁻³) 3 × 10¹⁸ 7 × 10¹⁷ [C](cm⁻³) 2 × 10¹⁸ 3 × 10¹⁷

With reference to Table X, as compared with the growth of a GaN crystal, the planar defect density in the {0001} plane of a GaN crystal could be markedly reduced in the growth of an additional GaN crystal (an additional Group III nitride crystal) while the crystal growth face was kept flat up to a higher crystal growth rate (below 150 μm/h) using an additional GaN crystal substrate (an additional Group III nitride crystal) prepared from a GaN crystal (Group III nitride crystal) (Example 54). Even at the crystal growth rate at which facets were formed on the crystal growth face, the planar defect density in the {0001} plane of the GaN crystal could be markedly reduced when all (four) of the impurity atom concentrations, that is, the oxygen atom concentration, the silicon atom concentration, the hydrogen atom concentration, and the carbon atom concentration, of the GaN crystal were in the predetermined range described above.

It is to be understood that the embodiments and examples disclosed herein are illustrated by way of example and not by way of limitation in all respects. The scope of the present invention is defined by the appended claims rather than by the description preceding them. All changes that fall within the scope of the claims and the equivalence thereof are therefore intended to be embraced by the claims.

Group III nitride crystals produced by a production method according to the present invention can be used in light emitting devices (such as light-emitting diodes and laser diodes), electronic devices (such as rectifiers, bipolar transistors, field-effect transistors, and high electron mobility transistors (HEMT)), semiconductor sensors (such as temperature sensors, pressure sensors, radiation sensors, and visible-ultraviolet photodetectors), surface acoustic wave (SAW) devices, acceleration sensors, micro electro mechanical systems (MEMS) components, piezoelectric vibrators, resonators, or piezoelectric actuators.

REFERENCE SIGNS LIST

1: Group III nitride bulk crystal; 10 p, 10 q, 20 p: Group III nitride crystal substrate; 10 pm, 10 qm, 20 m, 20 pm, 30 m: major surface; 10 pt, 10 qt: contact surface; 20, 30: Group III nitride crystal; 20 g, 30 g: crystal growth face; 20 gf, 20 mf, 30 gf, 30 mf: facet; 20 s, 30 s: region-on-substrate; 20 t, 30 t: region-on-substrate-interface; 20 tc: vertical plane; 20 v, 30 v: depression; 90: base substrate; 91: mask layer; 91 w: window 

What is claimed is:
 1. A method for producing a Group III nitride crystal, comprising the steps of: cutting a plurality of Group III nitride crystal substrates having a major surface from a Group III nitride bulk crystal, the major surface having a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}; transversely arranging the substrates adjacent to each other such that the major surfaces of the substrates are parallel to each other and each [0001] direction of the substrates coincides with each other; and growing a Group III nitride crystal on the major surfaces of the substrates.
 2. The method for producing a Group III nitride crystal according to claim 1, wherein the major surfaces of the substrates have a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−2−1} and {20−21}.
 3. The method for producing a Group III nitride crystal according to claim 1, wherein the average roughness Ra of each contact surface of the substrates adjacent to each other is 50 nm or less.
 4. The method for producing a Group III nitride crystal according to claim 1, wherein the method for growing the Group III nitride crystal is a hydride vapor phase epitaxy method.
 5. The method for producing a Group III nitride crystal according to claim 1, wherein in the step of growing a Group III nitride crystal the Group III nitride crystal is grown while the crystal growth face is kept flat.
 6. The method for producing a Group III nitride crystal according to claim 5, wherein in the step of growing a Group III nitride crystal on the major surfaces of the substrates: when the plane orientation of the major surfaces has an off-angle of five degrees or less with respect to {20−21}, the Group III nitride crystal has a growth rate below 80 μm/h; when the plane orientation of the major surfaces has an off-angle of five degrees or less with respect to {20−2−1}, the Group III nitride crystal has a growth rate below 90 μm/h; when the plane orientation of the major surfaces has an off-angle of five degrees or less with respect to {22−41}, the Group III nitride crystal has a growth rate below 60 μm/h; and when the plane orientation of the major surfaces has an off-angle of five degrees or less with respect to {22−4−1}, the Group III nitride crystal has a growth rate below 80 μm/h.
 7. The method for producing a Group III nitride crystal according to claim 1, wherein in the step of growing a Group III nitride crystal a Group III nitride crystal having at least one of the following impurity atom concentrations is grown: an oxygen atom concentration of 1×10¹⁶ cm⁻³ or more and 4×10¹⁹ cm⁻³ or less, a silicon atom concentration of 6×10¹⁴ cm⁻³ or more and 5×10¹⁸ cm⁻³ or less, a hydrogen atom concentration of 6×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less, and a carbon atom concentration of 1×10¹⁶ cm⁻³ or more and 1×10¹⁸ cm⁻³ or less.
 8. The method for producing a Group III nitride crystal according to claim 1, further comprising the steps of: preparing an additional Group III nitride crystal substrate having a major surface from the Group III nitride crystal, the major surface having a plane orientation with an off-angle of five degrees or less with respect to a crystal-geometrically equivalent plane orientation selected from the group consisting of {20−21}, {20−2−1}, {22−41}, and {22−4−1}; and growing an additional Group III nitride crystal on the major surface of the additional Group III nitride crystal substrate. 